What is a zombie computer ? - Security Term

A zombie computer, or “drone,” is a computer that has been secretly compromised by hacking tools which allow a third party to control the computer and its resources remotely. When the zombie computer connects to the Internet the remote hacker can clandestinely make contact with the computer to mine data from it or use it for any number of purposes. Communication between the hacker and the computer travels through back channels of the targeted system, keeping these processes hidden from the owner.